Generally, BNNT structures may be formed by thermally exciting a boron feedstock in a chamber in the presence of nitrogen gas at an elevated pressure. Unlike carbon nanotubes (CNTs), U.S. Pat. No. 8,206,674 to Smith et al., incorporated by reference in its entirety, indicates that BNNTs form without the presence of chemical catalysts, and preferably at elevated pressures of about 2 atm to about 250 atm. CNTs, on the other hand, typically require the presence of chemical catalysts such as metal catalysts. It has been shown that BNNTs do not form in the presence of such catalysts, indicating that the formation of BNNTs is fundamentally different than the formation of CNTs.
Most contemporary BNNT synthesis methods have severe shortcomings, including one or more of having low yield, short tubes, discontinuous production, poor crystallinity (i.e., many defects in molecular structure), and poor alignment. Although there is no agreed upon standard in the scientific literature, the term ‘high quality’ BNNTs generally refers to long, flexible, molecules with few defects in the crystalline structure of the molecule. However, there are no known reports of the growth of continuous BNNT fibers or BNNT strands, particularly having few defects and good alignment. The BNNT “streamers” described in U.S. Pat. No. 8,206,674 to Smith et al., for example, form near a nucleation site such as the surface of the boron feedstock, but were limited to about 1 cm in length. BNNT “streamers” at such lengths are inadequate for producing BNNT yarns.
What is needed are apparatus, systems, and methods for the continuous production of BNNT fibers and BNNT strands, having few defects and good alignment.